Many industrial furnaces such as smelting furnaces, blast furnaces, EAFs and the like typically have shells comprised of fluid-cooled metallic panels. The panels are cooled by conduits or channels extending through the panels that are connected to cooling circuits through which cooling fluid (typically water) is pumped and recirculated. Each panel has an inlet for the cooling fluid connected to the upstream end of the cooling circuit and an outlet for the cooling liquid connected to the downstream end of the cooling circuit.
Because of the high temperature and severe reaction conditions inside many industrial furnaces, furnace wall panels frequently develop leaks. However, isolating the leak to the particular cooling circuit in which the leak is located may be a cumbersome procedure when the cooling system contains several cooling circuits, as is often the case in modern industrial furnaces.
It is important to rapidly detect such leaks. Failure to do so may cause large volumes of cooling water to enter into the furnace. Water that becomes trapped under the molten metal quickly turns to steam resulting in a rapid expansion and subsequent explosion. These catastrophic events, though rare, can cause massive amounts of damage to the furnace and its surroundings. Alternatively, when the water in the leaky cooling member is at a pressure lower than the furnace internal gas pressure, failure to rapidly detect a leak may cause the loss of large amounts of furnace gas, often combustible gas, into the cooling circuit which may create serious safety problems. In addition, furnace gas entering the cooling system could be drawn into the pumping system and damage the pumps. Moreover, furnace gas leaking into, or steam generated in, a cooling plate that has or is about to fail may generate chain reaction damage in downstream cooling members in the circuit. That is, the temperature of the cooling fluid in downstream cooling members rises, thereby compromising the effectiveness of the cooling fluid in downstream cooling members which, in turn, may potentially cause a leak in one or more of those downstream members.
In certain prior art leak detection devices systems, one or more thermocouples are installed into the metal of the panels themselves. In the event the thermocouples detect a sudden change in panel metal temperature indicative of overheating, leak or rupture, an alarm is activated. The failure or simple delay in operation of a such a single-tier monitoring system may result in a water leak with potential attendant equipment damage and possible personal injury. As used herein, a “single-tier” monitoring system is a furnace panel leak detection system involving only one means or mechanism by which a coolant fluid leak may be detected. An example of a thermocouple-controlled industrial furnace roof panel is described in U.S. Pat. No. 4,813,055.
Another single-tier system is described in U.S. Pat. No. 4,455,017 wherein a thermostatically-controlled valve monitors panel temperature to control water flow through the panel by detecting the water temperature in the panel.
Another common single-tier leak detection system involves the use of water flow sensors for detecting changes in water flow in the panel which may be indicative of panel failure. Numerous types of flow sensors and associated instrumentation have been developed for measuring fluid flow. These sensors may include orifice meters, turbine meters, vortex meters, magnetic flow meters, and the like. One of these devices may be placed on the supply line of the cooling circuit and another one of may be placed on the return line of that circuit. The flow sensors detect differences in flow rates to determine if there is any leakage in the circuit between the inlet and outlet flowmeters. An example of such a system is described in U.S. Pat. No. 6,804,990.
U.S. Pat. No. 4,207,060 describes multiple-tier furnace wall panel leak detection system, although the system does not include thermocouples installed in the wall panels themselves for directly detecting the panel metal temperature. The system includes a cooling water supply line and a cooling water discharge line for recirculating cooling water through the furnace panels. The cooling water supply line includes a single water temperature sensor, a single water pressure sensor and a single water flow sensor. Following these sensors a check valve introduces the cooling water into each panel. Coolant water exiting each panel passes water temperature and pressure sensors, and thereafter a pressure relief valve, before passing through a check valve and into the cooling water return line. The system includes an alarm system and furnace shut down capability in the event a problem is detected in water temperature, pressure or flow. While an improvement over the single-tier furnace panel leak detection systems described above, the multiple-tier system disclosed in U.S. Pat. No. 4,207,060 nevertheless suffers from certain disadvantages.
For example, by their very nature, check valves present obstructions in the fluid line which cause sudden spike-like pressure drops in the fluid circuit when the check valve opening pressure is overcome. As seen in FIG. 3 of U.S. Pat. No. 4,207,060, the furnace panels include panels of different sizes that inherently produce different pressure drops at the inlets of each panel due to the different coolant volumes of the panels when the check valve trigger pressure is reached. Together, these variables at least temporarily affect the reliability of the data recorded by and observed from the panel outlet temperature and flow sensors. Moreover, the default “off” position of check valves tends to promote the buildup of foreign solid particles which could ultimately block the fluid circuit. Should clogging or mechanical failure occur in either the panel inlet or outlet check valve, water flow through the panel will be reduced or stopped, thereby leading to a rapid rise in panel temperature and possible harm to the panel, the furnace and the furnace surroundings. In addition, the provision of the coolant flow check valves at the outlets of the panels can cause water hammer damage to the coolant water return line into which they are discharged because of the sudden actuation nature typical of check valves.
Additionally, the presence of a single water temperature sensor, a single water pressure sensor and a single water flow sensor in the cooling water supply line upstream of the panels, i.e., before the coolant water reaches any of the panels, cannot provide an operator of the furnace with optimally accurate readings of the coolant water temperature, pressure and flow rate as it enters each panel. This is especially true of the panels most distant from the cooling water supply line sensors. The significance of this feature is that the downstream temperature and flow sensors compare panel water temperature versus coolant water temperatures and flows that may be rather distant therefrom, hence producing less than desirable comparative results.
Still further, the pressure relief valves at the outlets of the panels provide no meaningful data or information about conditions within the panels. Pressure relief valves are passive devices. They simply release pressurized coolant vapor or steam when a predetermined pressure has been reached. In this way, they are analogous to a check valve for fluid flow in that they suddenly function at a predetermined threshold level but are otherwise inoperative. As such, they are prone to clogging. Furthermore, they do not provide the furnace operator with real-time coolant panel outlet pressure data that may be useful in understanding and possibly anticipating malfunctions that might occur in a furnace panel during operation.
Lastly, the furnace wall panels of U.S. Pat. No. 4,207,060 consist of an elaborate array of serpentine pipes that are welded together and directly exposed to the intense heat of the interior of the furnace. Welds are notorious locations for cracks that may lead to water leakage. Additionally, despite the possibility that the surfaces of the pipes facing the interior of the furnace may become coated with slag during furnace operation and therefore afforded some level of thermal insulation, the substantial internal volume of the pipes—which constitutes the majority of the volume of the panels—requires that high quantities of coolant water be pumped through the pipes to maintain the panels at a desired temperature. This presents a problem at plant locations where coolant water is in limited supply and/or available at premium cost.
It is also known in the art to periodically manually check the pressure of coolant delivered to and from a furnace panel. However, manual monitoring is undesirable because of its inherent dependence upon the diligence and competence of a human operator coupled with the reliability of the equipment used to make the pressure measurements.
An advantage exists, therefore, for a furnace panel leak detection system that includes several tiers of coolant panel leak detection mechanisms, each of which actively and continuously monitor and report either the condition of the panel itself or the coolant that flows therethrough.
A further advantage exists for a system for periodically checking the water flow pressure through a furnace panel in order to identify potential coolant problems before they evolve into potentially dangerous situations. A preferred leak detection system will also allow for all panels to be thoroughly tested and checked for leaks and for water flow prior to turning on or starting the furnace as a sort of a pre-systems check.